Mutations in the mouse limb deformity (ld) locus disrupt embryonic pattern formation. This disruption leads to reduction and fusion of the distal bones and digits of all limbs and to variable incidence of renal aplasia. The ld locus contains evolutionarily conserved coding sequences which are transcribed in adult and embryonic tissues as a group of low abundance messenger RNAs created by alternative splicing and differential polyadenylation. Woychik, R. P. et al. (1990; Nature 346:850-853) deduced the structure of several novel proteins, termed formins, from the long open reading frames encoded by the ld transcripts. The presence of these RNA transcripts in a variety of tissues suggests that the formins play an essential role not only in limb and renal development but in the development of several organ systems (Woychik, et al., supra).
Formins are nuclear phosphoproteins which contain proline-rich sequences similar to Src homology 3 (SH3)-binding domains. The SH3 region is a small protein domain present in a large group of proteins, including cytoskeletal elements and signaling proteins. It is believed that SH3 domains serve as modules that mediate protein-protein associations and regulate cytoplasmic signaling. A fusion protein containing 28 amino acids from the proline-rich region of formin bound in vitro to the SH3 domains of the c-Src proto-oncogene (Ren, R. et al. (1993) Science 259:1157-1161). Ren et al. suggest that formins may function in development by interacting through their proline-rich sequences with SH3-containing proteins.
Chan, D. C. et al. (1996; EMBO J. 15:1045-1054) proposed that proteins which interact with formin via SH3-binding may play critical roles in development. They therefore used a proline-rich formin polypeptide to screen mouse limb bud expression libraries for proteins which interact with formin. Two groups of formin binding proteins (FBPs) were found: one group of FBPs contained SEH3 domains, and the second group of FBPs contained one or two copies of a newly characterized protein interaction domain, the WW domain.
The WW domain (also known as rsp5 or WWP) was originally identified as a short conserved region in a number of unrelated proteins, including dystrophin, the gene associated with Duchenne muscular dystrophy (Bork, P. et al. (1994) Trends Biochem. Sci. 19:531-533). The domain, which spans about 35 residues, is repeated up to 4 times in some proteins. The WW domain binds to certain proline-rich motifs and thus resembles the SH3 domain. The name WW or WWP derives from the presence of four conserved aromatic residues, generally tryptophans, and a conserved proline. It has been shown to interact with proline-rich domains typical of proteins involved in signal transduction processes (Bork, supra).
Chan et al. (supra) observed that the WW domain of certain FBPs can compete with the SH3 domain of Ab1 kinase for binding to the same proline-rich ligand. In view of their affinity for proline-rich SH3-binding ligands, Chan et al. suggested that WW domain-containing proteins may regulate the action of SH3 domain-containing proteins (such as the Src kinases) by modulating the interaction with SH3-binding ligands. Subsequently, Uetz, P. et al. (1996; J. Biol. Chem 271:33525-33530) demonstrated that chicken and mouse formins interact directly with Src family kinases c-Src and c-Fyn in vivo. This interaction was shown to occur through the formin proline-rich domain and the Src SH3 domain. Uetz et al. (supra) proposed that the molecular interaction of formins with Src family kinases links the formin molecules to the embryonic signaling cascades which are disrupted in ld mutant limb buds.
The discovery of a new human formin binding protein and the polynucleotides encoding it satisfies a need in the art by providing new compositions which are useful in the diagnosis, prevention and treatment of cancers and developmental and immune system disorders.